General thermodynamic law: volume effect on thermal properties and phase transition

Abstract

Recent studies show that there is a universal thermodynamic behavior in crystalline solids: the heat capacity is dependent on both of the temperature and thermal expansion (or volume). In glasses (or disordered materials), the heat capacity jump at glass transition is a typical feature, and is an important unsolved problem in solid state physics. There is not a quantitative interpretation for the volume effect on the heat capacity jump at glass transition at present. In this paper, we study the volume effect on the thermal behaviors in the typical Pd-based glass-forming alloy, and give an accurate interpretation between the change of the volume and the temperature dependent thermal properties. The crystalline and its disordered materials have same model parameters and same volume effect. Phase transition can be classified only by the corresponding relation between the volume and temperature. And the glass transition, a volume-induced thermal behavior, is a special phase transition between the classical first order and second order phase transitions. The thermal properties in materials with different states are well explained by the unified heat capacity model when the volume effect is considered, which shows that there a general thermodynamic rule in materials.